Steel alloy, holders and holder details for plastic moulding tools, and tough hardened blanks for holders and holder details

ABSTRACT

A steel alloy suitable for holders and holder details for plastic moulding tools contains in weight-%: 0.06-0.15 C, 0.07-0.22 N, wherein the total amount of C+N shall satisfy the condition, 0.16≦C+N≦0.26, 0.1-1.0 Si, 0.1-2.0 Mn, 12.5-14.5 Cr, 0.8-2.5 Ni, 0.1 1.5 Mo, optionally vanadium up to max. 0.7 V, optionally, in order to improve the machinability of the steel, one or more of the elements S, Ca and O in amounts up to max. 0.25 S, max. 0.01 (100 ppm) Ca, max. 0.01 (100 ppm) O, balance iron and unavoidable impurities.

TECHNICAL FIELD

[0001] The invention relates to a steel alloy and particularly to asteel alloy for the manufacturing of holders and holder details forplastic moulding tools. The invention also concerns holders and holderdetails manufactured of the steel, as well as blanks made of the steelalloy for the manufacturing of such holders and holder details.

BACKGROUND OF THE INVENTION

[0002] Holders and holder details for plastic moulding tools areemployed as clamping and/or framing components for the plastic mouldingtool in tool sets, in which tool the plastic product shall bemanufactured through some kind of moulding method. Among conceivableholder details there can be mentioned bolster plates and otherconstruction parts as well as heavy blocks with large recesses which canaccommodate and hold the actual moulding tool. Said holders and holderdetails are made of many different steel alloys, including martensiticstainless steels. A steel which is manufactured and marketed by theapplicant under the registered trade name RAMAX S® belongs to that groupand has the following nominal composition in weight-%: 0.33 C, 0.35 Si,1.35 Mn, 16.6 Cr, 0.55 Ni, 0.12 N, 0.12 S, balance iron and impuritiesfrom the manufacturing of the steel. The closest comparable standardizedsteel is AISI 420F. Steels of this type have an adequate corrosionresistance, but do not have a martensitic micro-structure which is ashomogenous that is desirable, but may contain ferrite and hard spots,which are due to retained, untempered martensite, which in turn can beexplained by a certain segregation tendency of the steel. Therefore itexists a demand of improvements as far as holder steels are concerned.It is also desirable that the same steel, possibly with somemodification of the composition, also shall be useful for the actualmoulding tool.

DISCLOSURE OF THE INVENTION

[0003] It is an object of the invention to provide a steel, which afterhardening and tempering has a more even structure than the abovementioned steel, essentially without ferrite and/or spots in thematerial which have a pronouncedly higher hardness.

[0004] The invention also aims to achieve one or several of thefollowing effects:

[0005] A good machinability.

[0006] An adequate corrosion resistance.

[0007] An adequate hardenability, considering the steel shall bepossible to be used for the manufacturing of holder blocks made ofplates which may have a thickness of up to at least 300 mm and in somecases even up to 400 mm thickness.

[0008] An adequate ductility/toughness.

[0009] A hardness of 30-42 HRC, preferably 38-40 HRC in thetough-hardened condition.

[0010] A good polishability, at least according to a preferredembodiment, in order to able to be used also for moulding tools on whichhigh demands are raised as far as polishability is concerned.

[0011] The above objectives can be achieved if the steel has thechemical composition which is stated in the appending patent claims.

[0012] As far as the importance of the separate elements and theirinteraction in the steel are concerned, the following may be consideredto apply without binding the claimed patent protection to any specifictheory.

[0013] Carbon and nitrogen are elements which have a great importancefor the hardness and ductility of the steel. Carbon is also an importanthardenability promoting element. Carbon, however, binds chromium in theform of chromium carbides (M7C3-carbides) and may therefore impair thecorrosion resistance of the steel. The steel therefore may contain max0.15% carbon, preferably max 0.13% carbon (in this text always weight-%is referred to if not otherwise is stated). However, carbon also hassome advantageous effects, such as to exist together with nitrogen as adissolved element in the tempered martensite in order to contribute tothe hardness thereof, and also acts as an austenite stabilizer andthence counteract ferrite in the structure. The minimum amount of carbonin the steel therefore shall be 0.06%, preferably at least 0.07%.

[0014] Nitrogen contributes to the provision of a more even, morehomogenous distribution of carbides and carbonitrides by affecting thesolidification conditions in the alloy system such that largeraggregates of carbides are avoided or are reduced during thesolidify-cation. The proportion of N23C6-carbides also is reduced infavour of M(C,N), i.e. vanadium-carbonitrides, which has a favourableimpact on the ductility/toughness. In summary, nitrogen contributes tothe provision of a more favourable solidification process implyingsmaller carbides and nitrides, which can be broken up during the workingto a more finely dispersed phase. From these reasons nitrogen shallexist in an amount of at least 0.07%, preferably at least 0.08%, but notmore than 0.22%, preferably max 0.15%, at the same time as the totalamount of carbon and nitrogen shall satisfy the condition 0.16≦C+N≦0.26.Preferably, C+N shall be at least 0.17% but suitably max 0.23%.Nominally, the steel contains 0.20-0.22 (C+N). In the hardened andtempered steel, nitrogen is substantially dissolved in the martensite inthe form of nitrogen-martensite in solid solution and thence contributesto the desired hardness.

[0015] In summary, as far as the content of nitrogen is concerned, itcan be stated that nitrogen shall exist in the said minimum amount inorder to contribute to the desired corrosion resistance by increasingthe so called PRE-value of the matrix of the steel, to exist as adissolved element in the tempered martensite which contributes to thehardness of the martensite, and to form carbonitrides, M(C, N), to adesired degree together with carbon, but not exceed said maximumcontent, maximizing the content of carbon+nitrogen, where carbon is themost important hardness contributor.

[0016] Silicon increases the carbon activity of the steel and thence thetendency to precipitate more primary carbides. This is a first reasonwhy it is desirable that the steel has a low content of silicon.Further, silicon is a ferrite stabilizing element, which is adisadvantageous feature of silicon. As the steel also shall contain theferrite stabilizing elements chromium and molybdenum in sufficientamounts to provide desirable effects by those elements, at the same timeas the steel contains a lower content of carbon than is conventional insteels for the application in question, the content of silicon should berestricted in order not to cause the steel to contain ferrite in itsmatrix. The steel therefore must not contain more that 1% Si, preferablymax. 0.7%.Si, suitably max. 0.5% Si, and most conveniently a still lowercontent of silicon. Generally the rule shall apply that the ferritestabilizing elements shall be adapted to the austenite stabilizing onesin order to avoid formation of ferrite in the steel. However, siliconexists as a residue from the desoxidation treatment, wherefore theoptimum content of silicon lies in the range 0.05-0.5%, normally in therange 0.1-0.4%, and is nominally about 0.2-0.3%.

[0017] Manganese is an element which promotes austenite andhardenability, which is a favourable effect of manganese, and can alsobe employed for sulphur refining by forming harmless manganese sulphidesin the steel. Manganese therefore shall exist in a minimum amount of0.1%, preferably at least 0.3%. Manganese, however has a segregationtendency together with phosphorous which can give rise totempering-embrittlement. Manganese therefore must not exist in an amountexceeding 2%, preferably max. 1.5%, suitably max. 1.3%.

[0018] Chromium is the main alloying element of the steel and isessentially responsible for provision of the stainless character of thesteel, which is an important feature of holders and holder details forplastic moulding tools, as well as for the plastic moulding tool itself,which often is used in damp environments, which may cause less corrosionresistant steels to rust.

[0019] Chromium also is the most important hardenability promotingelement of the steel. However, no substantial amounts of chromium arebound in the form of carbides, because the steel has a comparatively lowcarbon content wherefore the steel can have a chromium content as low as12.5% and nevertheless get a desired corrosion resistance. Preferablythe steel, however, contains at least 13.0% chromium. The upper limit isdetermined in the first place by the ferrite forming tendency ofchromium. The steel therefore must not contain more than max. 14.5% Cr,preferably max. 14.0% Cr. Nominally, the steel should contain 13.1-13.7%Cr.

[0020] Nickel should exist in the steel in a minimum amount of 0.8%,preferably at least 1.0%, in order to afford the steel a very highhardenability. From cost reasons, however, the content should be limitedto max. 2.5%, preferably to max. 2.0%. Nominally, the steel contains1.4-1.8% or about 1.6% Ni.

[0021] Optionally, the steel of the invention also may contain an activecontent of vanadium in order to bring about a secondary hardeningthrough precipitation of secondary carbides in connection with thetempering operation, wherein the tempering resistance is increased.Vanadium, when present, also acts as a grain growth inhibitor throughthe precipitation of MC-carbides. If the content of vanadium is toohigh, however, there will be formed large primary MC-carbonitridesduring the solidification of the steel, and this also occurs if thesteel is subjected to ESR-remelting, which primary carbides will not bedissolved during the hardening procedure. For the achievement of thedesired secondary hardening and for the provision of a favourablecontribution to the grain growth inhibition, but at the same timeavoiding formation of large, undissolvable primary carbides in thesteel, the optional content of vanadium should lie in the range0.07-0.7% V. A suitable content is 0.10-0.30% V, nominally about 0.2% V.Preferably, the steel also contains an active content of molybdenum,e.g. at least 0.1%, in order to give a hardenability promoting effect.Molybdenum up to an amount of at least 1.0% also promotes the corrosionresistance but may have effect also if the content is higher. Whentempering, molybdenum also contributes to increasing the temperingresistance of the steel, which is favourable. On the other hand, a toohigh content of molybdenum may give rise to an unfavourable carbidestructure by causing a tendency to precipitation of grain boundarycarbides and segregations. Besides, molybdenum is ferrite stabilizing,which is unfavourable. The steel therefore shall contain a balancedcontent of molybdenum in order to take advantage of its favourableeffects but at the same time avoid those ones which are unfavourable.Preferably, the content of molybdenum should not exceed 1.7%. An optimalcontent may lie in the range 0.1-0.9%, probably in the range 0.4-0.6%Mo.

[0022] Normally, the steel does not contain tungsten in amountsexceeding the impurity level, but may possibly be tolerated in amountsup to 1%.

[0023] The steel of the invention shall be possible to be delivered inits tough-hardened condition, which makes it possible to manufacturelarge sized holders and mould tools through machining operations. Thehardening is carried out through austenitizing at a temperature of850-1000° C., preferably at 900-975° C., or at about 950° C., followedby cooling in oil or in a polymer bath, by cooling in gas in a vacuumfurnace, or in air. The high temperature tempering for the achievementof a tough hardened material with a hardness of 30-42 HRC, preferably38-41 or about 40 SRC, which is suitable for machining operations, isperformed at a temperature of 510-650° C., preferably at 520-540° C.,for at least one hour, preferably through double tempering; twice fortwo hours. The steel may, as an alternative, be low temperature temperedat 200-275° C., e.g. at about 250° C., in order obtain a hardness of38-42 or about 40 HRC.

[0024] The steel may, according to a preferred embodiment, also containan active content of sulphur, possibly in combination with calcium andoxygen, in order to improve the machinability of the steel in its toughhardened condition. In order to obtain best effect in terms ofmachinability improvement, the steel should contain at least 0.07% S ifthe steel does not also contain an intentionally added amount of calciumand oxygen, and at least 0.035%, respectively, if the steel alsocontains an active amount of calcium and oxygen. The maximum sulphurcontent of the steel is 0.25%, when the steel is intentionally alloyedwith a content of sulphur. A suitable sulphur content in this case maybe 0.12%. Also a non-sulphurized variant of the steel, however, can beconceived.

[0025] In this case the steel does not contain sulphur above impuritylevel, and nor does that steel contain any active contents of calciumand/or oxygen.

[0026] It is thus conceivable that the steel may contain 0.035-0.25% Sin combination with 3-100 weight-ppm Ca, preferably 5-75 ppm Ca,suitably max. 40 ppm Ca, and 10-100 ppm O, wherein said calcium, whichmay be supplied as silicon-calcium, CaSi, in order to globulize existingsulphides to form calcium sulphides, counteracts that the sulphides geta non-desired, elongated shape, which might impair the ductility.

[0027] The steel of the invention can be manufactured conventionally ata production scale by manufacturing a metal melt in the normal way, saidmelt having a chemical composition according to the invention, andcasting the melt into large ingots or casting the melt continuously. Itis also possible to cast electrodes of the molten metal and thenremelting the electrodes through Electro-Slag-Remelting (ESR). It isalso possible to manufacture ingots powder-metallurgically throughgas-atomization of the melt to produce a powder, which then is compactedthrough a technique which may comprise hot isostatic pressing, so calledHIPing, or, as an alternative, manufacture ingots through sprayforming.

[0028] Further characteristics, aspects and features of the steelaccording to the invention, and its usefulness for the manufacturing ofholders and moulding tools, will be explained more in detail in thefollowing through a description of performed experiments and achievedresults.

BRIEF DESCRIPTION OF DRAWINGS

[0029] In the following description of performed experiments andachieved results, reference will be made to the accompanying drawings,in which

[0030]FIG. 1 shows a holder block of a typical design, which can bemanufactured of the steel according to the invention,

[0031]FIG. 2A is a chart showing the hardness of a first set of steels,produced in the form of so called Q-ingots (50 kg laboratory heats),after hardening but before tempering, versus the austenitizingtemperature at a holding time of 30 min,

[0032]FIG. 2B shows corresponding graphs for another number of testedsteels manufactured as Q-ingots,

[0033]FIG. 3A shows tempering curves for those steels in the first setwhich have been hardened from 1030° C.,

[0034]FIG. 3B shows the tempering temperature range 500-550° C. of thetempering curves of FIG. 3A at a larger scale, FIG. 3C shows temperingcurves within the tempering temperature range 500-550° C. for thosefurther tested steels, whose hardness versus the austenitizingtemperature was shown in FIG. 2B,

[0035]FIG. 4 is a chart which showing hardenability curves for thesteels which were tested as stated above,

[0036]FIG. 5 is a bar chart illustrating results from impact toughnesstesting of the above mentioned steels, and

[0037]FIG. 6A and FIG. 6B are bar charts which illustrate the criticalcurrent density, Icr, measured when corrosion testing samples which hadbeen slowly cooled in a vacuum furnace at two different cooling ratesfrom the austenitizing temperature and which thereafter had been hightemperature tempered to about 40 HRC.

EXAMINATION OF STEELS MANUFACTURED AT A LABORATORY SCALE

[0038]FIG. 1 shows a holder block 1 of a typical design, which shall bepossible to be manufactured of the steel according to the invention. Inthe block1 there is a cavity 2, which shall accommodate a mould tool,usually a plastic moulding tool. The block 1 has considerable dimensionsand the cavity 2 is large and deep. Therefore, a number of differentrequirements are raised on the material according to the invention, i.a.an adequate hardenability with reference to the considerable thicknessof the block and a good ability to be machined by means of cuttingtools, such as mill cutters and borers.

[0039] Material

[0040] 17 Q-ingots (50 kg laboratory heats) with compositions accordingto Table I were manufactured in four rounds. In the first round(Q9043-Q9080), ingots were manufactured having chemical compositionswithin a wide range; e.g. variants having comparatively high contents ofnitrogen were tested. It was revealed that the alloy having the mostinteresting features was Q9068, i.e. with carbon contents lying inmedium range around 0.10% and with moderate contents of nitrogen.

[0041] In the second round (Q9129-Q9132) one tried to optimize thefeatures that were obtained by Q9068. The carbon content was slightlyvaried, vanadium was added in order to obtain a finer grain size, andthe nickel content was lowered for one of the variants.

[0042] In the third round (Q9129-Q9139) variants having increasedsulphur contents were tested.

[0043] In a fourth round only two steels, Q9153 and Q9154, were testedin order to evaluate the relations between carbon and nitrogen.

[0044] The steels Q9043 and Q9063 are reference materials. Q9043 has acomposition according to SIS2314 and AISI 420, while Q9063 correspondsto W.Nr. 1.2316.

[0045] The Q-ingots were forged to the shape of rods of size 60×40 mm,whereupon the rods were cooled in vermiculite. TABLE I Test materials;chemical composition in weight-%, balance Fe and unavoidable impuritiesQ-ingot C N Si Mn Cr V Ni Mo S Q9043 0.36 0.026 0.83 0.47 13.9 0.32 0.180.12 n.a. Q9063 0.37 0.12 0.17 0.55 15.7 0.8 1.19 n.a. Q9064 0.27 0.180.14 1.35 16.7 0.3 1.61 0.44 n.a. Q9065 0.20 0.16 0.185 1.29 15.7 0.151.56 0.74 n.a. Q9067 0.11 0.063 0.18 1.1 12.3 0.73 0.33 n.a. Q9068 0.110.059 0.17 1.06 13.4 0.067 2.1 0.75 n.a. Q9069 0.075 0.084 0.15 1.0112.4 0.076 0.75 0.34 n.a. Q9070 0.076 0.085 0.18 1.14 13.8 0.06 0.740.32 n.a. Q9080 0.15 0.17 0.21 1.26 16 0.12 1.56 0.75 n.a. Q9129 0.0970.087 0.16 1.06 12.8 0.2 1.6 0.22 n.a. Q9131 0.11 0.088 0.15 1.07 12.70.19 0.86 0.22 n.a. Q9132 0.14 0.094 0.14 1.11 12.7 0.19 1.61 0.22 n.a.Q9135 0.19 0.039 0.12 0.93 13.4 0.27 1.02 0.21 0.07 Q9136 0.07 0.0910.15 1.17 14.9 0.22 1.04 0.21 0.075 Q9139 0.12 0.092 0.17 1.23 14.2 0.201.06 0.22 0.14 Q9153 0.12 0.10 0.14 0.81 12.7 0.20 1.58 0.24 0.0059Q9154 0.06 0.14 0.17 0.88 12.5 0.21 1.53 0.21 0.0053

[0046] Hardness after Heat Treatment

[0047] The hardness versus the austenitizing temperature is shown inFIG. 2A and FIG. 2B. It is evident from the charts of these drawingsthat the hardness increases with increasing austenitizing temperaturefor some steels having a higher carbon content, such as for Q9043,Q9063, Q9103, Q9104 and Q9135. 1030° C. is an austenitizing temperaturewhich may be appropriate in these cases. For other steels, the hardnessdecreases or remains constant with increasing austenitizing temperature.In that case it may be more appropriate to choose 950° C. as anaustenitizinc temperature.

[0048] The hardness after tempering of those steels which had beenhardened from 1030° C. are shown in FIG. 3A and FIG. 3B, while all thetempering curves for those ones of the Q-ingots 9129-9154 which had beenhardened from 950° C. are shown in the diagram in FIG. 3C. Theconclusion can be drawn from the tempering curves that all the steelscan be tempered down to 40 ERC through tempering in the temperaturerange 520-600° C.

[0049] An appropriate hardness of the steel after tough-hardening isabout 40 BRC. In Table II below, the heat treatments are stated whichprovide the said hardness to the different steels. TABLE III Heattreatment for tough-hardening, measured rest austenite, percent byvolume Q-ingot Rest austenite No Heat treatment (%) 9063 1030° C./30min + 550° C./2 × 2 h 0 9064 1030° C./30 min + 550° C./2 × 2 h 1.3 90651030° C./30 min + 550° C./2 × 2 h 2.3 9067 1030° C./30 min + 525° C./2 ×2 h 0 9068 1030° C./30 min + 525° C./2 × 2 h 0 9069 1030° C./30 min +525° C./2 × 2 h 0 9070 1030° C./30 min + 525° C./2 × 2 h 0 9080 1030°C./30 min + 550° C./2 × 2 h 6.4 9104 1030° C./30 min + 550° C./2 × 2 h 09129* 950° C./30 min + 525° C./2 × 2 h 0 9131* 950° C./30 min + 525°C./2 × 2 h + 535/2 h 0 9132* 950° C./30 min + 525° C./2 × 2 h + 535/2 h0 9135* 950° C./30 min + 525° C./2 × 2 h 0 9136* 950° C./30 min + 525°C./2 h + 500/2 h 0 9139* 950° C./30 min + 525° C./2 × 2 h 0 9153** 950°C./30 min + 525° C./2 × 2 h 0 9154 950° C./30 min + 525° C./2 × 2 h Notmeasured

[0050] Hardenability

[0051] The hardness after hardening from the austenitizing temperatureswhich are given in Table II, from which temperatures the samples havebeen cooled at different rates, is shown in the hardenability curves ofFIG. 4.

[0052] Impact Toughness Tests

[0053] Impact toughness testing of un-notched test specimens, meanvalues for four to six test rods of each steel, was performed at roomtemperature. The heat treatments and cooling rates, which were employedfor the different steels, are given in Table III. The results aredisclosed by the bar chart in FIG. 5. From this chart it can berecognized that some varients, such as Q9067, 9068, 9069, 9129, 9131,9132 and Q9153 have a very high ductility, >350 J, and that the testrods were not ruptured, but also that some other steels, including e.g.steel Q9154, have a considerably better ductility than the referencesteels, Q9063 and 9043, which lie on the 180-200 J level. TABLE IIIQ-ingot No Heat treatment ° C. Cooling rate t8/5 (s) 9043 1030/30 +560/2 h + 550/2 h 2093 9063 1030/30 + 570/2 h + 560/2 h 2093 9064950/30 + 560/2 × 2 h 2093 9065 950/30 + 550/2 × 2 h 2093 9067 950/30 +525/2 × 2 h 2093 9068 950/30 + 525/2 × 2 h 2093 9069 950/30 + 525/2 × 2h 2093 9070 950/30 + 525/2 × 2 h 2093 9080 950/30 + 550/2 × 2 h 20939129 950/30 + 550/2 × 2 h 1969 9131 950/30 + 525/2 × 2 h + 535/2 h 19699132 950/30 + 525/2 × 2 h + 535/2 h 1969 9135 950/30 + 525/2 × 2 h 19649136 950/30 + 525/2 × 2 h + 500/2 h 1964 9139 950/30 + 525/2 × 2 h 19649153 950/30 + 535/2 × 2 h 1985 9154 950/30 + 540/2 × 2 h 1863

[0054] Corrosion Tests

[0055] Polarization curves were established in a first test round forthe steels given in Table IV in terms of critical current density, Icr,for the evaluation of the corrosion resistance of the steels. As far asthis method of measurement is concerned, the rule is that the lower Ircis, the better is the corrosion resistance. The investigations wereperformed in two test series, in which the test specimens were subjectedto different cooling rates. The heat treatments of the first series areshown in Table IV. TABLE IV Heat treatment of polarization testspecimens. Cooling in vacuum furnace Q- Hard- ingot T8/5 ness No Heattreatment (s) (HRC) 9063 1030° C./30 min + 570° C./2 × 2 h 860 40.8 90641030° C./30 min + 600° C./2 × 2 h 860 40.5 9065 1030° C./30 min + 580°C./2 × 2 h 860 40.0 9067 1030° C./30 min + 525° C./2 × 2 h + 535° C./1 h860 38 9068 1030° C./30 min + 525° C./2 × 2 h 860 40.1 9069 1030° C./30min + 525° C./2 × 2 h + 535° C./1 h 860 40 9070 1030° C./30 min + 525°C./2 × 2 h + 535° C./1 h 860 39 9080 1030° C./30 min + 565° C./2 h +550°C./2 h 860 40.6 9129 950° C./30 min + 525° C./2 h + 535°/2 h 876 39.79131 950° C./30 min + 525° C./2 h + 535° C./2 h 876 40.2 9132 950° C./30min + 535° C./2 × 2 h 876 39.7 9153 950° C./30 min + 535° C./2 × 2 h 95739.4

[0056] The results from this first test round are evident from the barchart in FIG. 6A. From this bar chart it is evident that five steels hada better corrosion resistance than the reference material, Q9063, namelyQ9068, Q9070, Q9129, Q9132 and Q9153.

[0057] Still slower cooling rates t8/5 were employed in a second testround, see Table V and FIG. 6B. TABLE V Heat treatment of polarizationtest specimens. Cooling in vacuum furnace Q- Hard- ingot T8/5 ness NoHeat treatment (s) (HRC) 9063 1030° C./30 min + 570° C./2 × 2 h 188038.9 9104 1030° C./30 min + 570° C./2 × 2 h 1880 40.1 9129 950° C./30min + 525° C./2 × 2 h 1969 40.6 9131 950° C./30 min + 525° C./2 × 2 h +535° C./2 h 1969 39.6 9132 950° C./30 min + 525° C./2 × 2 h + 535° C./2h 1969 40.1 9135 950° C./30 min + 525° C./2 + 2 h 1964 40.9 9136 950°C./30 min + 525° C./2 h + 500° C./2 h 1964 39.0 9139 950° C./30 min +525° C./2 × 2 h 1964 42.1 9153 950° C./30 min + 535° C./2 × 2 h 188540.3 9154 950° C./30 min + 540° C./2 × 2 h 1863 39.0

[0058]FIG. 6B illustrates that best corrosion resistances were notifiedfor samples of Q9063, 9129, 9153 and 9154.

[0059] Discussion

[0060] In the introductory disclosure of the invention there were listeda number of purposes of the invention. Besides a good machinability, thesteel shall have a good ductility, a good corrosion resistance, and agood hardenability. It can be stated that it is an aim that the steel,besides a good machinability, shall have better ductility, corrosionresistance and hardenability than steel Q9063. Four steels satisfy thosecriteria, namely Q9068, Q9129, Q9153 and Q9154, which have a rathersimilar composition; although steel Q9154 has a higher nitrogen contentand a lower content of carbon. On the basis of these experiences, it canbe assumed that an optimal composition could be the following, namely0.10 C, 0.075 N, 0.16 Si 1.1 Mn, 13.1 Cr, 0.13 V, 1.8 Ni, 0.5 Mo,balance Fe and unavoidable impurities. An alternative could be a steelwhich contains 0.06 C and 0.14 Ni but as for the rest the samecomposition as the foregoing. Other alternatives—suitably conceivablenominal compositions—could be the following ones: 0.12 C, 0.20, 0.10 S,13.4 Cr, 1.60 N1, 0.50 Mo, 0.20 V, 0.10 N, balance iron and unavoidableimpurities, and/or 0.14 C, 0.18 Si, 1.30 Mn, 0.10 S. 13.5 Cr, 1.67 Ni,0.50 Mo, 0.22 V, 0.10 N, balance iron and unavoidable impurities.

[0061] Manufacturing of Steel at a Production Scale

[0062] A 35 tons heat of molten metal was manufactured in an electricarc furnace. Before tapping, the melt had the following chemicalcomposition: 0.15 C, 0.18 Si, 0.020 P, 0.08 S, 13.60 Cr, 1.60 Ni, 0.48Mo, 0.20 V, 0.083 N, balance Fe and unavoidable impurities. Of the meltthere were manufactured ingots, which were forged to the shape of flatrods of varying dimensions. The forging did not cause any problems. Theforged rods were tough-hardened to a hardness of about 380 BB throughaustenitizing at 950° C., holding time 2h, fast quenching in air andtempering at 540° C., 2×2 h. The thus tough-hardened rods were machinedto final gauges.

1. A steel alloy, characterized in that it has a chemical compositionwhich contains in weight-%: 0.06-0.15 C 0.16≦C+N≦0.26 0.1-1.0 Si 0.1-2.0Mn 12.5-14.5 Cr 0.8-2.5 Ni 0.1-1.5 Mo optionally vanadium up to max. 0.7V optionally one or more of the elements S, C and 0 in order to improvethe machinability of the steel, in amounts up to max. 0.25 S, max. 0.01(100 ppm) Ca, max. 0.01 (100 ppm) O, balance iron and unavoidableimpurities.
 2. A steel alloy according to claim 1, characterized in thatit contains 0.07-0.13 C.
 3. A steel alloy according to claim 1,characterized in that ft contains 0.08-0.15 N.
 4. A steel alloyaccording to any of claims 1-3, characterized in that the total amountof C+N shall satisfy the condition 0.17<C+N<0.23.
 5. A steel alloyaccording to claim 1, characterized in that it contains 0.1-0.7 Sipreferably max. 0.5 Si.
 6. A steel alloy according to claim 5,characterized in that it contains 0.1-0.4 Si.
 7. A steel alloy accordingto claim 1, characterized in that it contains max. 1.5 Mn, preferablymax. 1.3 Mn.
 8. A steel alloy according to claim 1, characterized inthat it contains 13.0-14.0 Cr.
 9. A steel alloy according to claim 8,characterized in that it contains 13.1-13.7 Cr.
 10. A steel alloyaccording to claim 1, characterized in that it contains 1.0-2.0 Ni. 11.A steel alloy according to claim 10, characterized in that it contains1.4-1.8 Ni.
 12. A steel alloy according to claim 1, characterized inthat it contains 0.1-0.9 Mo.
 13. A steel alloy according to claim 12,characterized in that it contains 0.4-0.6 Mo.
 14. A steel alloyaccording to claim 1, characterized in that it contains at least 0.07 V.15. A steel alloy according to claim 14, characterized in that itcontains at least 0.10 V.
 16. A steel alloy according to claim 15,characterized in that it contains 0.10-0.30 V.
 17. A steel alloyaccording to claim 1, characterized in that it contains max.
 0. 15 S.18. A steel alloy according to claim 17, characterized in that itcontains 0.08-0.12 S.
 19. A steel alloy according to claim 1,characterized in that it does not contain S, Ca or O above impuritylevel.
 20. A steel alloy according to any of the preceding claims,characterized in that it contains 0.06-0.13 C 0.08-0.15N 0.1-0.4,preferably 0.2-0.3 Si 0.2-1.3 Mn 12.5-13.6 Cr 0.1-0.3 V 0.2-0.8 Mo1.4-1.8 Ni
 21. Holders and holder details for plastic moulding tools,characterized in that they consist of a steel alloy according to any ofclaims 1-20 .